This is the revision of the last renewal of a technology resource grant (P41) entitled A Resource on Medical Ultrasonic Transducer Technology. It was funded at Penn State University in 1997 to pursue innovative research in high frequency (HF) ultrasonic transducers and arrays as well as to serve the medical ultrasound community who has a need for such transducers and arrays. In 2002 the Resource was moved to USC and renewed in 2005. In the past 5 years, significant progress has been made in transducer materials, HF single element transducers and arrays, and imaging electronics, resulting in 101 refereed publications and 10 patents or patent disclosures. In addition, a new initiative on studying the feasibility of ultrasound microbeams defined as ultrasound beams at frequencies higher than 200 MHz was launched. Novel piezoelectric thin/thick films have been developed allowing ultrahigh frequency (UHF) transducers (200 MHz -1 GHz) to be designed and built. HF linear arrays at 30 MHz have been improved to consist of now 256 elements and a curved linear array at 20 MHz for imaging posterior side of the eye has been developed. Prototype real-time analog and digital HF imaging platforms are fully functional. Exploratory experiments on ultrasound microbeam for trapping cells, cell sorting, cellular mechanotransduction, and acoustic radiation force imaging of microstructures were carried out, demonstrating that exciting opportunities exist for ultrasound to play a more significant role in the promising field of cellulr bioengineering. There have been 17 collaborative projects and 8 service projects. In next grant period, there will be four internal core projects: (I) hovel transducer materials and UHF transducers (II) HF arrays and imaging platforms, (III) ultrasound microbeam, and (IV) novel piezoelectric materials and HF material characterization along with 15 collaborative projects and 4 service projects. The major thrusts of the core research will be (1) to develop UHF single element transducers for microbeam applications, (2) to develop a 35 MHz phased array and imaging platform for cardiac imaging in small animals, (3) to develop linear arrays at 50 MHz and higher and curved linear arrays in the 15 - 20 MHz range, and (4) to exploit cellular applications of ultrasound microbeams.